1. Curs an IV limba engleza 2012-2013
HEMOSTAZA
Curs an IV limba engleza

2. HEMOSTASIS
Hemostasis is defined as a property of circulation whereby blood is maintained within a vessel and the ability of the system to prevent excessive blood loss when injured.
Process is rapid and localized

3. HEMOSTASIS Hemostasis can be divided into two stages
Primary hemostasis
Response to vascular injury
Formation of the “platelet plug” adhering to the endothelial wall
Limits bleeding immediately
Secondary Hemostasis
Results in formation of a stable clot
Involves the enzymatic activation of coagulation proteins that function to produce fibrin as a reinforcement of the platelet plug
Gradually the stable plug will be dissolved by fibrinolysis

4. HEMOSTASIS
Following an injury to blood vessels several actions may help prevent blood loss, including:
Formation of a clot

5. HEMOSTASIS The primary players in hemostasis include
Blood vessels
Platlets
Plasma proteins
Coagulation proteins – involved in clot formation
Fibrinolysis – involved in clot dissolution
Serine protease inhibitors
Other minor players include
Kinin system
Complement system

6. VASCULAR SYSTEM
Smooth and continuous endothelial lining is designed to facilitate blood flow
Intact endothelial cells inhibit platelet adherence and blood coagulation
Injury to endothelial cells promotes localized clot formation
Vasoconstriction
Narrows the lumen of the vessel to minimize the loss of blood
Brings the hemostatic components of the blood (platelets and plasma proteins) into closer proximity to the vessel wall
Enhances contact activation of platlets
Von Willebrand factor
Collagen fibers
Platlet membrane glycoprotein Ib
Activated platlets enhance activation of coagulation proteins

7. LOCAL VASOCONSTRICTION
is due to local spasm of the smooth muscle (symp. reflex)
can be maintained by platelet vasoconstrictors

8. PRIMARY HEMOSTASIS Platelets Primary platelet plug
Interact with injured vessel wall
Interact with each other
Produce the primary hemostatic plug
Primary platelet plug
Fragile
Can easily be dislodged from the vessel wall

9. PLATLET FUNCTION
Provide negatively charged surface for factor X and prothrombin activation
Release substances that mediate vasoconstriction, platlet aggregation, coagulation, and vascular repair
Provide surface membrane proteins to attach to other platlets, bind collagen, and subendothelium

10. ADHESION
Damage to endothelium exposes blood to the subepithelial tissue matrix with adhesive molecules
Platlet receptor GPIb binds to subendothelium collagen fibers through von Willebrand’s factor (vWF)
Platlet adherence stops the initial bleeding

11. ADHESION

12. SHAPE CHANGE
Following vessel injury and platlet exposure to external stimuli, platlets change shape from circulating discs to spheres with pseudopods
Exposure of platlet membrane phospholipids promotes the assembly of vitamin-K dependent factors on the platlet membrane surface
Activated platlets adhere to exposed collagen

13. AGGREGATION Platlet-to-platlet interaction
Begins seconds after vascular injury and platlet adhesion
Requires dense granule release from the adhering platlets
Requires Ca++ and ATP
Requires fibrinogen and fibrinogen receptors GPIIb and IIIa
Mechanism:
ADP released from platlet cytoplasm upon adherence induces exposure of fibrinogen receptors GPIIb and IIIa
Fibrinogen binds to the exposed GPIIb and IIIa
Extracellular Ca++-dependent fibrinogen bridges form between adjacent platlets, thereby promoting platlet aggregation
This is primary or reversible aggregation
Secondary aggregation begins with the release of dense granules
Secondary aggregation is considered irreversible

14. SECRETION
Secondary aggregation begins with platlet secretion of dense granules
Dense granules contain large amounts of ADP
ADP binds to the platlet membrane triggering the synthesis and release of TXA2
The release of large amounts of ADP combined with TXA2 amplifies the initial aggregation of platlets into a large platlet mass

15. PRIMARY HEMOSTASIS

16. SECONDARY HEMOSTASIS Also called the fibrin forming coagulation system
The purpose is to reinforce the platlet plug
System mediated by many coagulation factors present in an inactive form in blood.
Factors are assigned Roman numerals, I through XIII
Assigned in order of discovery, not place in reaction sequence
Each one has one or more common names or synonyms
Roman numeral followed by letter “a” indicates the activated form of the factor
All are produced in the liver. The von Willebrand factor is also produced in endothelial cells and megakaryocytes.

17. SECONDARY HEMOSTASIS The cascade theory of blood coagulation
Involves a series of biochemical reactions
Transforms circulating substances into an insoluble gel through conversion of fibrinogen to fibrin
Requires
Plasma proteins
Phospholipids
calcium

18. COAGULATION - CASCADE THEORY
Each coagulation factor is converted to an active form by the preceeding factor in the cascade
Calcium participates in some of the reactions as a co-factor
The blood coagulation cascade occurs on cell surface membranes.

19. COAGULATION - CASCADE THEORY
Clotting factors bind to the phospholipid membrane surface and rearrange until a complex including enzyme, substrate, and cofactor is formed.
Subendothelial tissue exposed with vascular injury and platlet surface provide the critical membranes
The membrane localizes the reaction to the site of injury

20. SECONDARY HEMOSTASIS
Three different complexes assemble on the phospholipid membrane
The pathways for the formation of these complexes are
Intrinsic
Extrinsic
Common -Both intrinsic and extrinsic pathways converge to share factors in the common pathway
Both intrinsic and extrinsic pathways require initiation
Intrinsic - all factors involved in clot formation are in the vascular compartment
Extrinsic- is initiated when a tissue factor not found in blood enters the vascular system

21. EXTRINSIC PATHWAY
The extrinsic pathway is initiated when there is an injury to a blood vessel wall
In the presence of the tissue factor released from the injured nonvascular tissue (factor III or thromboplastin) and calcium (factor IV), factor VII is activated to factor VIIa
Factor VIIa activates factor X to Xa
Factor VIIa can also activate factor IX in the intrinsic pathway to IXa

22. EXTRINSIC PATHWAY

23. INTRINSIC PATHWAY
Is initiated following exposure to negatively charged foreign substances such as collagen, subendothelium, or phospholipids.
Factor XII is activated to XIIa.
XIIa then interacts with the contact factors, prekallikrein and kininogen, to activate Factor XI to XIa
XIa then activates Factor IX to IXa in the presence of Ca++
IXa participates along with co-factor VIII:C, Ca++, and PF3 (a source of phospholipids), to activate Factor X which leads to the generation of thrombin
IXa -factor VIIIa-phospholipid-Ca++ is called the tenase complex

24. INTRINSIC PATHWAY
The complex of IXa, VIIIa, X, PF3,and Ca++ assembles on the surface of activated platlets (supply the phospholipid).
The surface provides the protective environment for the enzymatic reactions to occur
In plasma, VIII circulates as a complex in association with C which has the procoagulant activity and von Willebrand factor (vWF) which functions as a carrier protein.
VIII requires enhancement by the generated enzyme thrombin to amplify its activity

25. Intrinsic Pathway PTT Partial Thromboplastin Time VIIIa+Ca+Pl Va+Ca+Pl
XII XIIa
XI XIa
IX IXa
VIIIa+Ca+Pl
X Xa
Va+Ca+Pl
II IIa
Fibrinogen Fibrin

26. COMMON PATHWAY Intrinsic and extrinsic pathways
Converge on the common pathway
Both pathways activate Factor-X to Xa
Xa in the presence of Factor V, Ca++ and phospholipid converts prothrombin (Factor II) to its active form thrombin (IIa)
Thrombin then feeds back to activate factors VIII and V, converts fibrinogen to soluble fibrin, and helps to stabilize the fibrin monomer by converting factor XIII to XIIIa.
XIIIa cross-links the fibrin monomers to form a stable fibrin polymer

27. FIBRINOGEN 3 stages of conversion of fibrinogen to fibrin Proteolysis
Thrombin cleavage of fibrinogen results in fibrin monomers
Polymerization
Spontaneous self-assembly into fibrin polymers
Stabilization
Introduction of covalent bonds into fibrin polymers by XIIIa

28. COAGULATION

29. THE CLOT

30. FIBRINOLYSIS
The last stage of coagulation is fibrinolysis, which is the dissolution and localization of a fibrin clot.
Prevents excessive fibrin deposition
Allows closely coupled with fibrin formation
Localized surface bound phenomenon that is catalyzed by fibrin formation

31. FIBRINOLYSIS
Fibrinolytic system is a complement to the coagulation system – a fine balance between the two systems must occur
Restricts fibrin formation to area of injury
Dissolves clot by digestion of fibrin
Initiated when coagulation begins – will ultimately dissolve clot
plasminogen ↓
Fibrin plasmin → fibrin degradation products (FDPs)

32. FIBRINOLYSIS - COMPONENTS
Plasminogen -> plasmin
Plasminogen activators
Inactivators of plasminogen
Inhibitors of plasmin

33. FIBRINOLYSIS
Plasminogen is activated and converts to plasmin by factor XII, HMWK,and PK
Plasmin = enzyme which dissolves fibrin clots into protein fragments that are cleared from plasma by the liver
Fibrin degradation products are breakdown fragments of fibrin or fibrinogen.
The protein fragments are designated X, Y, D, and E
Fragments are strong inhibitors of further coagulation by
interfering with the action of thrombin
interfering with platelet aggregation

34. FIBRINOLYSIS Inhibitors of fibrinolysis = antiplasmins.
Used to regulate and limit plasmin activity and fibrinolysis
alpha-2-antiplasmin
alpha-2-macroglobulin

36. FIBRINOLYSIS

37. FIBRINOLYSIS

38. HEMOSTATIC BALANCE
The regulation of hemostatic and fibrinolytic processes is dynamic
Balance between
Pro- and anti-hemostatic mediators
Pro- and anti-fibrinolytic mediators
Balance can be upset if any components are
Inadequate
Excessive
Development of thrombi
Excessive local or systemic activation of coagulation
Sustained bleeding
Excessive local or systemic fibrinolytic activity

39. ANTICOAGULANTS
Although tissue breakdown and platelets destruction are normal events in the absence of trauma, intravascular clotting does not usually occur because:
the amounts of procoagulants released are very small
natural anticoagulants are present (Antithrombin III, Heparin, Antithromboplastin, Protein C and S, fibrin fibers)

40. NATURAL ANTICOAGULANTS
Antithrombin III – inhibits factor X and thrombin
Heparin from basophils and mast cells potentiates effects of antithrombin III (together they inhibit IX, X, XI, XII and thrombin)
Antithromboplastin (inhibits „tissue factors” – tissue thromboplastins)
Protein C and S – activated by thrombin; degrade factor Va and VIIIa

41. HEMOSTATIC BALANCE When hemostasis is delayed
Either platelet disorder or a coagulation defect
Bleeding episode may be prolonged
Imbalance created between
An abnormally slow hemostatic rate
A normal rate of fibrinolysis
An inadequate fibrinolytic response
May retard lysis of a thrombus and even contribute to its extension

42. LABORATORY EVALUATION OF HEMOSTASIS
Bleeding disorders present differently depending upon the causative problem
Platlet disorders present as petechiae and bleeding into mucous membranes because of failure to form the platlet plug
Patients with coagulation defects may develop deep spreading hematomas and bleeding into the joints with evident hematuria because of failure to reinforce the platlet plug.

43. LABORATORY EVALUATION
Three different categories of disorders may be found
Vascular and platlet disorders
Coagulatioin factor deficiencies or specific inhibitors
Fibrinolytic disorders

44. LABORATORY EVALUATION
Tests to differentiate between these include
Platlet count
Peripheral blood smear evaluation
Ivy bleeding time (N= min) or platlet function analyzer (PFA)
Prothrombin time (PT) – test contains thromboplastin and calcium chloride and measures measures the extrinsic and common pathways (Normal=11-13 sec)

45. LABORATORY EVALUATION
Activated partial thromboplastin time (APTT) -contact activators and a platlet substitute and calcium chloride are added to measure the intrinsic and common pathways (Normal usually sec, may vary depending upon analyzer used, reagents used, and patient population)
Thrombin time (TT) – add thrombin and measure the time required for thrombin to convert fibrinogen to fibrin (common pathway) (N=15-22 sec)

46. LABORATORY EVALUATION
Mixing studies with PT and APTT abnormal results -patient plasma is mixed with normal plasma to distinguish between factor deficiencies and coagulation inhibitors
If assay is corrected – due to factor deficiency
If partially corrected or uncorrected – due to inhibitor
Coagulation factor assays
Assays for fibrin degradation products – evidence of fibrinolysis